The present invention relates generally to agricultural machinery and, more particularly, to improvements to harvesting machines. The improvement relates specifically to a sensor for detecting structure-borne noise vibrations, which are generated by the impingement of harvested material on a pulse detector, and to means for improving and monitoring the operation of the sensor.
A sensor is known from German Patent 24 48 745. To measure the lost grains at the discharge ends of straw walkers and in grain separation or cleaning devices, steeply inclined pulse detector plates are attached via damping members over the entire conveyor width. An elector-acoustic converter is attached to the underside of these plates by means of a spring clamp. The residual or lost grains present in the flow of material drop onto the pulse detector plates and cause vibrations, which the pulse detector plates convey to the electro-acoustic converter. The plates are connected via the converter casing to a microphone and convert the vibrations into an electrical signal. The vibrations are transmitted over a plurality of coupling points. Due to its construction and the manufacturing steps entailed therewith, as well as the influences of corrosion, dirt and other items, each coupling point represents a weak point in the sensor. The signal sensitivity of this sensor is therefore inconsistent and is subject to fluctuations determined by aging.
Another loss sensor is known from German Patent 37 31 080. This sensor has only one coupling point. A piezo quartz is attached directly to the counter side of the pulse detector surface. The connection between the piezo quartz and a striker surface is produced by means of a soldering or adhesive point. This connection has at least a few serious drawbacks. When there are large mechanical or thermal stresses on the pulse detector surface, such as those which may occur during cleaning, adjustment or repair of the screens or walkers, the property of the adhesive or soldered connection to couple sound vibrations is altered. Furthermore, with such a connection, aging phenomena are of importance. These alterations are difficult to understand or detect and require the intervention of a specialist for their monitoring. Under certain circumstances, the connection may be destroyed by foreign bodies impinging on the striker surface. Reinstatement of the connection requires complete dismantling and recalibration of the sensor. Therefore for reasons of time and technical skill, in most cases of breakdown the entire sensor is changed, which leads to unnecessary costs.
There is known from the European Patent 0 339 142 a sensor which has a plurality of coupling points. In this sensor the converter is inserted between two plates, using a plurality of elastic components and a signal damping layer, and are screwed together by means of a plurality of screws. This converter pack is then brought into contact by an additional screw connection to the actual pulse detector. The screw connections must be so disposed that the converter is not exposed to any stresses, and abuts flat on the contact plates 35. Therefore the converter pack and the converter are screwed together, but with a space between the two. A consequence of this is a large connecting area between the converter pack and the pulse detector. Influences such as dust, deformations in the pulse detector and moisture, or a changeover of converter, may alter the connecting surfaces. The larger the connecting surfaces, the less reliable the prediction of the actual size of the connecting surfaces. It therefore cannot be predicted how large the connecting surfaces are at any moment. The signal sensitivity is inconsistent and it cannot be ensured over the duration of the full life of the device. The construction and attachment is extremely complicated, requiring the assistance from a specialist during first assembly and repair.
Furthermore, no methods or means are known by which the operation of the sensor can be monitored. Object underlying the present invention are therefore to provide a sensor of the type already described, which removes the described drawbacks, has defined coupling points between the pulse detector and the piezo electric converter, and is of a simple and reliable construction.